A high-speed precision motion platform is widely used in the fields of semiconductor encapsulation and the like. Uncertain change of surface roughness between motion pairs in the high-speed precision motion platform causes uncertain change of amplitude of frictional resistance. However, in processes of starting, stop and micro feeding of the motion platform, the speed of the motion platform is relatively low and fluctuation of the amplitude of the above frictional resistance is easy to cause a “crawl” phenomenon of the motion platform. Under the action of a closed-loop control system, a driver overcomes the frictional resistance by increasing the driving force to compensate for a positioning error of the motion platform. In the above compensation process, the motion platform will experience frequent “static-moving” state switching. In the “static-moving” process, the frictional resistance between the motion pairs experiences “static frictional force-moving frictional force” state switching. However, sudden change of the acceleration at a moment of the state switching is caused by a difference between a static friction coefficient and a moving friction coefficient, thereby causing “jitter” of the motion platform near a final position location and influencing positioning accuracy.
How to reduce a positioning error influence caused by switching of frictional states in the processes of starting, stop and micro feeding is an important problem that affects execution accuracy of the high-speed precision motion platform. In view of the above problem, the following solutions exist at present:
1. An accurate frictional force model is established, and a manner of controlling driving force compensation by motion is adopted:
2. The design of frictionless or low-friction motion pairs is adopted. For example, structural designs of an air floatation bearing, a magnetic levitation bearing or flexible hinges of a micro feeding platform are adopted.
Because of such factors as microscopic property difference of contact surfaces, manufacturing errors and the like between the motion pairs, it is difficult to establish a highly accurate frictional force model, so that a complex compensation control method needs to be adopted in a motion control system.
Implementation cost of low-friction motion pairs of the air floatation bearing or the magnetic levitation bearing and the like is high, thereby limiting use ranges.
The flexible hinges as external frictionless motion pairs realize continuous high-accuracy motion by means of elastic deformation. Due to the limit of an operation principle, flexible hinge motion pairs are mainly applicable to micro-stroke motion. In occasions of large-stroke motion, the flexible hinges are often used together with friction motion pairs to form a macro-micro composite motion platform to realize large-stroke high-accuracy motion, so as to compensate for large-range motion.
Patent application CN1201410696217.0 proposes a linear motor co-stator dual-drive macro-micro integrated high-speed precision motion one-dimensional platform. A macro-moving outer frame and a micro-moving platform of the proposed macro-micro motion platform are respectively connected with two groups of linear motor movers, wherein the macro-moving outer frame and the micro-moving platform are connected through flexible hinges; the macro-moving outer frame realizes large-stroke macro motion under the drive of a corresponding linear motor mover; and the micro-moving platform dynamically compensates for a motion deviation of the above macro motion under the drive of a corresponding linear motor mover. The large-stroke high-accuracy motion is realized by using the above macro-micro composite motion principle. Because the design of frictionless flexible hinge motion pairs is adopted in the micro-moving platform of the motion platform, continuous displacement change in a positioning process is realized. The motion platform proposed in patent application CN201410696217.0 has the following main disadvantages: (a) because macro-micro composite control is adopted, a macro-moving platform and the micro-moving platform of the motion platform need respective drivers and displacement sensors to form feedback systems, causing high cost; (2) switching control of the macro motion and the micro motion needs to be considered in the control system, causing that the control system is complex; (3) the mass of a motion part in the platform is large, which is not beneficial for use in occasions under a large-inertia influence such as high acceleration and the like; and (4) the feedback control system of the macro-moving platform still needs to consider the influence of the frictional state in a positioning phase to ensure that a displacement deviation of the macro-moving platform is less than an ultimate deformation range of the flexible hinge motion pairs in the positioning process.